In optoelectronic applications optical links have to be provided to connect different optical components of an optical device or to connect different optical devices with each other. Multi-core optical fibers allow for high density optical links that can be used inside optical devices to connect different optical components or between different optical devices. However, the density of the fiber cores makes the connection to an optical device difficult. When connecting two optical components like VCSELS or photodiodes the size of the optical component dictates the spacing of the separate connections. Typical component sizes are on the order of 200 μm, while the distance between the optical cores inside an optical fiber is generally lower than 100 μm. This means that multi-core optical fibers cannot be used to connect these optical components without modification of the multi-core optical fiber or application of an intermediate step using additional optical components.
It is believed that in the future a plurality of optical devices will be manufactured by the Silicon Photonics technology. As used herein, “Silicon Photonics” means using a chip such as an integrated circuit (IC) having the ability for receiving optical signal along with the electronic functionality in the chip, for example a chip with silicon or III/V-materials. The advantages of Silicon Photonics are reduced space and power requirements concurrent with increased speed and lower costs. These photonic structures on an optical chip still have to be connected to the outer devices through optical waveguides such as optical fibers. However, using separate fibers, for example with a diameter of about 125 μm, for each connection requires much more space than the counterpart silicon photonic structures which have, for example, a diameter of about 200 nm, and thus partly cancels the effect of miniaturization.
The application of a multi-core optical fiber for coupling to an optical chip including optical devices made by the Silicon Photonics technology can help to conserve the high density packing of the photonic structures by increasing the connection density, for example by arranging eight optical cores in the diameter of an ordinary optical fiber. Since the Silicon Photonics technology allows the integration of optical components on a very small scale, the spacing of the optical cores of a multi-core optical fiber determines the distances of the optical connections.
This works well for edge-coupled fibers where all optical waveguides terminate at the edge of the chip at distances matched to the spacing of the optical cores in the multi-core optical fiber. However, the coupling of a multi-core optical fiber with, for example, linearly arranged optical cores in two rows to an optical chip via the edge of the chip has certain disadvantages, since the differences in the size of the structures are quite large. An optical core of a multi-core optical fiber has a diameter of about 10 μm while the waveguide on the chip has a diameter of about 200 nm, which creates a mismatch.
A size conversion of the mode field has to take place as the mode field is confined to the order of 100 nm while an optical core of the optical fiber has a size of about 10 μm. This means that coupling from the optical chip into the optical fiber works well, while the reverse is not true. Matching the mode fields requires a lot of space on the optical chip, negating the advantages of the miniaturization of the Silicon Photonics technology.
An alternative method is the use of grating couplers that are edged into the surface of an optical chip and can be tailored to match the size of an optical core of an optical fiber without sacrificing too much additional space. However, the direct coupling of the face of the optical fiber to the surface of the optical chip requires the fiber to stick out from the surface. The fiber may be bent, for example by 90°, to be guided away from the optical chip and to be connected to a different device or may be bent by an angle of 180° when it is to be attached to another part of the same optical chip.
It is desirable to provide a multi-core optical fiber which allows for a reliable coupling to an optical chip and a space-saving arrangement of the optical fiber when coupling the optical fiber to an optical chip. It is a further desire to provide an optical system which allows for a reliable and space-saving coupling of a multi-core optical fiber to an optical chip. A further concern is to provide a method of manufacturing a multi-core optical fiber which allows for a reliable and space-saving coupling of the optical fiber to an optical chip.
An embodiment of a multi-core optical fiber which enables a reliable coupling to an optical chip and concurrently a space-saving arrangement is defined in present application. According to an embodiment of the multi-core optical fiber, the optical fiber comprises a plurality of optical cores to respectively transmit light, the optical cores extending in the multi-core optical fiber along a longitudinal axis of the multi-core optical fiber and comprising a first optical core and at least a second optical core being different from the first optical core. The multi-core optical fiber further comprises a plurality of cleaves extending from a surface of the multi-core optical fiber into the multi-core optical fiber and comprising a first cleave and at least a second cleave being different from the first cleave. The first cleave comprises a surface, wherein the first optical core ends at the surface of the first cleave. The surface of the first cleave is configured to deflect the light transmitted in the first optical core such that the light is coupled out of the multi-core optical fiber at the surface of the first cleave. The at least one second cleave comprises a surface, wherein the at least one second optical core ends at the surface of the at least one second cleave and wherein the surface of the at least one second cleave is configured to deflect the light transmitted in the at least one second optical core such that the light is coupled out of the multi-core optical fiber at the surface of the at least one second cleave. The first and the at least one second cleave are staggered along the longitudinal axis of the multi-core optical fiber.
An optical system which enables a multi-core optical fiber to be coupled to an optical chip in a reliable and space-saving manner is defined in claim 11. According to an embodiment of the optical system, the system comprises a multi-core optical fiber as described above and an optical chip comprising a substrate and a first optical device and at least a second optical device being respectively disposed on the substrate. The multi-core optical fiber is arranged above the optical chip such that the longitudinal axis of the multi-core optical fiber is arranged in a plane being parallel to a plane of the substrate as far as the end of the multi-core optical fiber. The multi-core optical fiber is arranged above the optical chip such that light coupled out of the first optical core of the multi-core optical fiber is coupled into the first optical device and/or light coupled out of the first optical device is coupled into the first optical core of the multi-core optical fiber. The multi-core optical fiber is arranged above the optical chip such that light coupled out of the at least one second optical core of the multi-core optical fiber is coupled into the at least one second optical device and/or light coupled out of the at least one second optical device is coupled into the at least one second optical core of the multi-core optical fiber.
A method of manufacturing a multi-core optical fiber which allows for a reliable coupling of the fiber to an optical chip and concurrently for a space-saving arrangement of the fiber when coupled to the optical chip is defined in claim 13. According to the method a multi-core optical fiber is provided, wherein the multi-core optical fiber includes a plurality of optical cores to respectively transmit light, wherein the optical cores extend in the multi-core optical fiber along a longitudinal axis of the multi-core optical fiber and wherein the optical fiber comprises a first optical core and at least a second optical core being different from the first optical core. A plurality of cleaves extending from a surface of the multi-core optical fiber into the multi-core optical fiber and comprising a first cleave and at least a second cleave being different from the first cleave are created. The first cleave comprises a surface, wherein the first optical core ends at the surface of the first cleave and wherein the surface of the first cleave is configured to deflect the light transmitted in the first optical core such that the light is coupled out of the multi-core optical fiber at the surface of the first cleave. The at least one second cleave comprises a surface, wherein the at least one second optical core ends at the surface of the at least one second cleave and wherein the surface of the at least one second cleave is configured to deflect the light transmitted in the at least one second optical core such that the light is coupled out of the multi-core optical fiber at the surface of the at least one second cleave. The first and the at least one second cleave are staggered along the direction of the longitudinal axis of the multi-core optical fiber.
The disclosure is also directed to a multi-core optical fiber, comprising a plurality of optical cores extending in the multi-core optical fiber along a longitudinal axis of the multi-core optical fiber and comprising a first optical core and at least a second optical core being different from the first optical core and a cladding where the plurality of optical cores are embedding in the cladding. The multi-core optical fiber further comprises a plurality of cleaves extending from a surface of the multi-core optical fiber into the multi-core optical fiber and comprising a first cleave and at least a second cleave being different from the first cleave. The first cleave comprises a surface, wherein the first optical core ends at the surface of the first cleave. The surface of the first cleave is configured to deflect the light transmitted in the first optical core such that the light is coupled out of the multi-core optical fiber. The at least one second cleave comprises a surface, wherein the at least one second optical core ends at the surface of the at least one second cleave and wherein the surface of the at least one second cleave is configured to deflect the light transmitted in the at least one second optical core such that the light is coupled out of the multi-core optical fiber. The first and the at least one second cleave are staggered along the longitudinal axis of the multi-core optical fiber and the cladding is shaped such that the multi-core optical fiber comprises at least one alignment structure to align the multi-core optical fiber onto a surface.
The disclosure is also directed to a multi-core optical fiber, comprising a plurality of optical cores extending in the multi-core optical fiber along a longitudinal axis of the multi-core optical fiber and comprising a first optical core and at least a second optical core being different from the first optical core wherein the first optical core is disposed in a first array and the second optical core is disposed in a second array. By way of explanation, the first core is disposed in a first linear array as a first row and the second core is disposed in a second linear array as a second row. However, the first and second array may have other arrangement such as non-linear array or the like. The multi-core optical fiber further comprises a plurality of cleaves extending from a surface of the multi-core optical fiber into the multi-core optical fiber and comprising a first cleave and at least a second cleave being different from the first cleave. The first cleave comprises a surface, wherein the first optical core ends at the surface of the first cleave. The surface of the first cleave is configured to deflect the light transmitted in the first optical core such that the light is coupled out of the multi-core optical fiber. The at least one second cleave comprises a surface, wherein the at least one second optical core ends at the surface of the at least one second cleave and wherein the surface of the at least one second cleave is configured to deflect the light transmitted in the at least one second optical core such that the light is coupled out of the multi-core optical fiber. The first and the at least one second cleave are staggered along the longitudinal axis of the multi-core optical fiber.
The disclosure is also directed to a multi-core optical fiber, comprising a plurality of optical cores extending in the multi-core optical fiber along a longitudinal axis of the multi-core optical fiber and comprising a first optical core and at least a second optical core being different from the first optical core. The multi-core optical fiber further comprises a plurality of cleaves extending from a surface of the multi-core optical fiber into the multi-core optical fiber and comprising a first cleave and at least a second cleave being different from the first cleave. The first cleave comprises a surface, wherein the first optical core ends at the surface of the first cleave. The surface of the first cleave is configured to deflect the light transmitted in the first optical core such that the light is coupled out of the multi-core optical fiber. The at least one second cleave comprises a surface, wherein the at least one second optical core ends at the surface of the at least one second cleave and wherein the surface of the at least one second cleave is configured to deflect the light transmitted in the at least one second optical core such that the light is coupled out of the multi-core optical fiber. The first and the at least one second cleave are staggered along the longitudinal axis of the multi-core optical fiber and the first cleave comprises another surface, and the other (e.g., another) surface extends between the surface of the first cleave and the surface of one of the at least one second cleave.
The staggered cleaves or kerfs allow an adjustable spacing of the light spots coupled out of the optical cores of the multi-core optical fiber. This allows an in-plane arrangement of the optical fiber as well as a tailoring of the distances between the coupling sites to the requirements of the optical devices arranged on an optical chip or a printed circuit board. With the method described above only the material directly in front of each core is removed. The material may be removed such that each of the kerfs is provided with a slanted surface in relation to the direction of the optical cores, for example, a 45° angle cleave. The local kerfs are offset with respect to each other in order to allow for the space requirements of the optical devices that the multi-core optical fiber is coupled with for reliable and efficient communication of the optical signals.
It is to be understood that both the foregoing general description and the following detailed description present embodiments and are intended to provide an overview or a framework for understanding the nature and character of the disclosure. The accompanying drawings are included to provide a further understanding, and are incorporated into and constitute a part of this specification. The drawings illustrate various embodiments and, together with the description, serve to explain the principles and operation of the concepts disclosed.